1. Field of the Invention
This invention relates to fastening devices, and more particularly to fastening devices which are particularly and specifically adapted for use in an open-sided synthetic resin box for receiving and retaining screws employed to secure a cover plate across the open side of the box.
2. Brief Description of the Prior Art
In United States patent application Ser. No. 528,007, entitled "Electrical Wall Box", and assigned to the assignee of the present application, an electrical wall box construction is disclosed in which a synthetic resin electrical wall box is formed to provide slots adjacent an open side of the wall box. Spring metal inserts are pressed into these slots, and function to receive and engage screws employed to secure a cover plate over the open side of the electrical wall box. The spring metal inserts utilized are of generally V-shaped configuration, having a pair of divergent legs joined through a bend, and further characterized in having a circular aperture formed in one of the legs, and a tongue pressed out of the other of the two legs. The leg which carries the tongue has a pair of lateral edge skirts or flanges which are bent out of the main plane of this leg of the insert, and function to assist in wedging this leg of the insert into the receiving slot formed in the synthetic resin wall box so as to retain the insert or fastener in position during use.
The metal insert or fastener illustrated and described in the co-pending application is further constructed so that the tongue which is pressed out of one leg of the V-shaped metal insert projects toward the other leg of the insert by a distance which is greater than the distance measured across the bent connecting portion utilized to connect the two legs of the insert. Stated differently, the tongue pressed out of the one leg of the metal insert projects a distance from the major plane of this one leg, as measured normal to this plane, which is always at least two-thirds of the distance which the leg-connecting bend portion of the insert projects from the major plane of this one leg, also as measured in a direction normal to this major plane.
In the course of using the described spring metal inserts in electrical wall boxes having an open side, and for the purpose of engaging and retaining screws extended through the aperture formed in one of the legs of such inserts, it has been found that the pressure which is developed by the tine or tongue-bearing leg upon the synthetic resin of which such boxes are constructed tends to distort the resin over a short period of usage of the insert in the slot provided, with the result that the metal inserts become loose in the slots in a shorter period of time, and lose their effective screw-retaining ability. Moreover, as a result of the formation of the lateral edge skirts or flanges bent out of the major plane of the leg of the insert which is inserted in the slot in the box, the total surface area of this leg which is in contact with one side of the slot is reduced, further increasing the looseness of the clip in the slot following a short period of usage for screw retention.
It has also been experienced that the formation of these lateral edge skirts or flanges which are bent out of the major plane of the leg of the insert which is pressed into the slots in the box, causes a greater rigidity in the bend which interconnects the two legs of the insert than is desirable, in that the leg carrying the screw-receiving hole then cannot flex easily, and to the extent desired, when the screws are pressed into the hole in the insert so as to accommodate the screw, and achieve the ratcheting, screw-retaining action which must be accomplished by such metal inserts. Further, the inclusion of the bends at the flanges or skirts at the sides of the leg placed in the slot in the box appears to make the other screw-receiving leg more susceptible to permanent distortion from its initial angle when it is flexed away from this angle by the force of a screw being pressed through the aperture for purposes of engagement. Such permanent distortion results in poor screw engagement and retention, with subsequent looseness or eventual loss of the cover plate from the electrical wall box.